Add Runner interface.

pre_commit/runner.py

@@ -0,0 +1,42 @@
+
+import os
+import os.path
+
+import pre_commit.constants as C
+from pre_commit import git
+from pre_commit.clientlib.validate_config import load_config
+from pre_commit.repository import Repository
+from pre_commit.util import cached_property
+
+
+class Runner(object):
+    """A `Runner` represents the execution context of the hooks.  Notably the
+    repository under test.
+    """
+
+    def __init__(self, git_root):
+        self.git_root = git_root
+
+    @classmethod
+    def create(cls):
+        """Creates a PreCommitRunner by doing the following:
+            - Finds the root of the current git repository
+            - chdirs to that directory
+        """
+        root = git.get_root()
+        os.chdir(root)
+        return cls(root)
+
+    @cached_property
+    def hooks_workspace_path(self):
+        return os.path.join(self.git_root, C.HOOKS_WORKSPACE)
+
+    @cached_property
+    def config_file_path(self):
+        return os.path.join(self.git_root, C.CONFIG_FILE)
+
+    @cached_property
+    def repositories(self):
+        """Returns a tuple of the configured repositories."""
+        config = load_config(self.config_file_path)
+        return tuple(map(Repository, config))